1. Field of the Invention
The present invention relates to an adaptive filter.
2. Description of the Related Art
In an adaptive filter, a step size parameter μ having a great value may be used to reduce a convergence time period for a filter coefficient to converge to a proper value. However, when the step size parameter μ is unnecessarily increased in value, the filter coefficient may not consequently converge and may significantly deviate from its optimal value. Thus, the value of the step size parameter μ is determined considering the balance between whether the filter coefficient converges in value and the convergence time period (see, e.g., Japanese Laid-Open Patent Publication No. 2002-261528).
For example, an adaptive filter configured to operate based on a CMA (Constant Modulus Algorithm) has a filter coefficient whose update amount varies with not only the step size parameter μ but also the amplitude of an output signal outputted from the adaptive filter. The amplitude of the output signal outputted from the adaptive filter varies with the amplitude of an input signal inputted to the adaptive filter. Therefore, when the amplitude of the input signal inputted to the adaptive filter significantly fluctuates, it is difficult to properly control the update amount of the filter coefficient.